Copying machine of the penetration printing type

ABSTRACT

In a copying machine wherein an original sheet to be copied and a photosensitive copy sheet are carried in superposed relation on the surface of a transparent rotating cylinder, teeth for gripping the leading edge of the original sheet to prevent dislocation thereof are mounted for rotation adjacent to, and in synchronism with rotation of, the cylinder surface. Signalresponsive means for selectively opening and closing the teeth are disposed at spaced localities around the cylinder to control engagement and release of the original sheet by the teeth. The teeth are rotated by means that arrest them at the end of each complete revolution until a sensor detects passage of the trailing end of the original in the path of sheet advance. The machine is operable to conduct an original through a predetermined number of successive revolutions before releasing it, for production of a corresponding number of copies; initiation of each successive revolution of the original begins only when the trailing edge of the original has passed a point at which the original has been fully copied.

Unite States Patent [1 1 Kobayashi 1 May28, 1974 COPYING MACHINE OF THE PENETRATION PRINTING TYPE [75] Inventor: Yugoro Kobayashi, Tokyo, Japan [73] Assignee: Ricoh Co., Ltd., Tokyo, Japan [22] Filed: Nov. 6, 1972 211 Appl. No.: 303,864

[30] Foreign Application Priority Data Nov. 17, 1971 Japan 4691456 [52] U.S. Cl 355/109, 355/l 10, 271/53 [51] Int. Cl. G03b 27/12 [58] Field of Search t. 355/107, 106, lO8, 109, 355/110; 271/53 MG [56] References Cited UNITED STATES PATENTS 2,371,925 3/1945 Schade et a1. 355/110 3,380,365 4/1968 Umahashi 355/110 X 3,409,356 11/1968 Robertson et a1. 355/110 X 3,432,236 3/1969 Vercoulen 355/109 Primary Examiner-Richard M Sheen Attorney, Agent, or FirmCooper, Dunham, Clark,

Griffin & Moran V V V [57] ABSTRACT In a copying machine wherein an original sheet to be copied and a photosensitive copy sheet are carried in superposed relation on the surface of a transparent rotating cylinder, teeth for gripping the leading edge of the original sheet to prevent dislocation thereof are mounted for rotation adjacent to, and in synchronism with rotation of, the cylinder surface. Signalresponsive means for selectively opening and closing the teeth are disposed at spaced localities around the cylinder to control engagement and release of the original sheet by the teeth. The teeth are rotated by means that arrest them at the end of each complete revolution until a sensor detects passage of the trailing end of the original in the path of sheet advance. The machine is operable to conduct an original through a predetermined number of successive revolutions be fore releasing it, for production of a corresponding number of copies; initiation of each successive revolution of the original begins only when the trailing edge of the original has passed a point at which the original has been fully copied.

7 Claims, 9 Drawing Figures COPYING MACHINE OF THE PENETRATION PRINTING TYPE BACKGROUND OF THE INVENTION This invention relates to copying machines, and more particularly it is concerned with a copying machine of the penetration printing type comprising a printing cylinder, a belt passed around the outer periphery of the printing cylinder for rotating it and conveying a photosensitive sheet and an original superposed one on the other as a unit, automatic means for feeding photosensitive sheets, and repeat means including an originalcirculating path.

In the copying art sometimes termed penetration printing, an original sheet to be copied and a photosensitive copy sheet superposed contiguously thereon are illuminated from one side to form an image of the original on the copy sheet, which may then be subjected to operations for rendering the image visible and pennanent. Typically the original and copy sheet are pressed against a transparent rotating cylinder for rotary movement therewith, and are illuminated from within the cylinder as they advance. To produce plural copies, the original is rotated repeatedly with the cylinder while successive copy sheets are fed to the cylinder.

When a copying operation is automatically performed in a copying machine of the character described, with the machine preset at a required number of photosensitive sheets to be exposed, difficulty has often been encountered in performing the operation positively and efficiently. This has been especially the case when the number of photosensitive sheets to be exposed is great. The original which is repeatedly moved along its circulating path has often tended to be deflected from its normal path of movement or inclined in its position during its movement, resulting in the original not being duplicated in the correct position on the photosensitive sheets, so that, in extreme cases, the image may be only partially reproduced on the photosensitive sheets.

SUMMARY OF THE INVENTION The present invention has as its object the provision of a copying machine of the character described which obviates the aforementioned disadvantage of the prior art.

The invention contemplates the provision, in a copying machine of the penetration printing type, of grip means for holding the leading end portion of an original in gripping relationship and rotatable along the outer periphery of the printing cylinder in synchronism therewith, such grip means responding to signals supplied from outside to move between an open position and a closed position so as to hold and release the leading end portion of the original as desired. The use of the gripper means provided by this invention permits the original to be held positively and accurately at all times and prevented from being deflected from its normal path of movement or inclined in its position during its movement.

According to the invention, means are also provided for sensing the trailing end portion of the original, arranged in the path of movement of the original and a photosensitive sheet superposed one on the other along the outer periphery of the printing cylinder, and means for causing the gripper means to stand by in its starting position till the trailing end portion of the original is sensed by the sensing means. The provision of these means permits duplication of the original to be effected without any trouble even if the original has a length greater than the outer circumference of the printing cylinder.

Other and additional objects as well as features and advantages of the invention will become evident from the description set forth hereinafter when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view in explanation of a copying machine in its entirely incorporating an embodiment of this invention therein;

FIG. 2 is a fragmentary view of the copying machine shown in FIG. 1, showing the gripper means in its starting position;

FIG. 3 is a view similar to FIG. 2 but showing the gripper means in its position during a printing operatron;

FIG. 4 is a view similar to FIG. 2 but showing the gripper means in its position after completion of the repeat;

FIG. 5 is a sectional view showing the printing cylinder, gripper means holding ring support mechanism and gripper means actuating mechanism;

FIG. 6 is a plan view of the structure shown in FIG.

FIG. 7 is a view in explanation of the gripper means actuating mechanism;

FIG. 8 is a fragmentary perspective view of the mechanism shown in FIG. 7; and

FIG. 9 is a connection diagram showing the electric elements used in the invention.

DETAILED DESCRIPTION In FIG. 1, a conveyor belt 4 is trained about a drive roller 2 and a plurality of guide rollers 3 and passed around a portion of the outer periphery of a transparent printing cylinder 1 which houses therein a built-in light source 5. If an original 7 is inserted in an original receiving slit, a photosensitive strip will be automatically fed by means indicated schematically at SE from a photosensitive roll 8A and a photosensitive sheet 8 (FIG. 2) of a size corresponding to the size of the original 7 is severed by a cutter 17 from the photosensitive strip 8C.

The original 7 and photosensitive sheet 8 move through different paths till they reach the vicinity of the printing cylinder 1 where the original 7 is gripped by gripper means 9 according to this invention and superposed on the photosensitive sheet, The original and the photosensitive sheet superposed one on the other are pressed against the outer periphery of the printing cylinder l by the belt 4 and rotate with the printing cylinder 1. While the original and the photosensitive sheet are rotating with the printing cylinder, printing is effected by means of light emanating from the light source 5.

Upon completion of printing, the exposed photosensitive sheet 8 is separated from the original 7 by being drawn by the action of a suction tank 10, developed at a developing station 11, and ejected onto a copy sheet receiving tray 12. Elements 13 and 14 are a belt for discharging an original and a suction tank respectively, while 15 is a tray for receiving an ejected original.

The original 7 is held by the gripper means 9 till a predetermined number of photosensitive sheets are exposed. Upon completion of production of a predetermined number of duplicates, teeth 9A and 9B of the gripper means 9 are opened as shown in FIG. 4 to release the leading end portion of the original, which is then drawn by the action of the suction tank 14 to the belt 13 and ejected onto the original receiving tray 15. Preferably, the teeth 9A and 9B are made of a transparent material and have a small thickness so that they do not interfere with the printing operation.

In FIG. and FIG. 6, the transparent printing cylinder 1 is shown as being rotatably supported by three flanged rollers 16 arranged equidistantly from one another and disposed around the outer periphery of the cylinder 1, the cylinder 1 being rotated as aforementioned by the conveyor belt 4 passed around a portion of its outer periphery.

A pair of rings 18 for holding the gripper means 9 are rotatably supported at both the end portions of the cylinder I by three flanged rollers 19 arranged equidistantly from one another and disposed around the outer periphery of the cylinder 1. The rings 18 are driven from the drive of the copying machine through a sprocket wheel 20, a gear 21, and a serration 18A'of each ring 18 which is maintained in meshing engagement with the gear 21, for rotation in synchronism with the printing cylinder 1. A control connection 22 having an electromagnetic clutch and a brake built therein is connected between the gear 21 and the sprocket wheel to rotate the rings 18 when an electric signal is produced (by means not shown in FIGS. 5 and 6) and render the same stationary when an electric signal is not produced, or when another electric signal is produced.

In FIG. 7, the gripper holding rings 18 are shown as having a shaft 23 rotatably mounted thereon and having the teeth 9A and an arm 24 firmly secured thereto. The teeth 9B are pivotally mounted on the shaft 23 (see FIG. 8). The shaft 23, teeth 9A and arm 24 form a unit which is urged to pivot clockwise in FIG. 7 and FIG. 8 by the biasing force of a spring 25 acting on the arm 24 which has a roller 26 attached to its forward end. The teeth 9B are urged to pivot counterclockwise by the biasing force of a spring (not shown).

A control lever 27 is pivotally supported at a stationary pivot point 28 and connected at its free end to a plunger 29A of a solenoid 29. The roller 26 is urged by the biasing force of the spring 25 into engagement with the control lever 27 at all times, i.e., when the ring 18 carries the roller 26 into the illustrated position adjacent lever 27. The solenoid 29 is controlled by a counter 30, and when the supply of a current to the solenoid 29 is cut off, all the parts of the aforementioned gripper means actuating mechanism are in broken line positions and the teeth 9A and 9B hold the leading end portion of an original therebetween.

As shown in FIG. 7, the gripper means actuating mechanism is provided in two sets along the gripper holding ring 18, the lower set comprising a control lever 27 and a solenoid 29' (similar in arrangement and operation to the above-described lever 27 and solenoid 29) being disposed in an original gripping position shown in FIG. 2 and the upper set being disposed in an original release position shown in FIG. 4. The lower set has a pushbutton switch 31 attached thereto.

Sensing means 32 for sensing the movement of the original 7 and the photosensitive sheet 8 superposed one on the other is arranged as shown in FIG. 7 at a preselected location along the path of movement thereof. The sensing means 32 produces and supplies a signal to the counter 30 when it senses the movement of the unitary original and photosensitive sensitive sheet (see also FIG. 9).

In operation, the original 7 is inserted between the open teeth 9A and 9B of the gripper means 9 which is in the open position as shown in FIG. 2, and the pushbutton switch 31 shown in FIG. 7 and FIG. 9 is depressed. This passes a current to the solenoid 29' which is energized and (by moving the lever 27 thereby to permit movement of the gripper teeth by the biasing forces acting thereon) brings the teeth 9A and 93 into engagement with one another to hold the leading end portion of the original therebetween. At the same time, a current is passed to the electromagnetic clutch of the control connection 22 shown in FIG. 5 and FIG. 9, so that the gripper means holding ring 18 begins to rotate in synchronism with the printing cylinder 1.

The photosensitive sheet 8 severed from the photosensitive strip roll 8A by the cutter 17 is moved through means (not shown) to a position in which the original 7 is superposed on the photosensitive sheet 8 and conveyed by the belt 4 to move along the outer periphery of the printing cylinder 1. During this movement, an image of the original 7 is printed on the photosensitive sheet 8 by light emanating from the light source 5.

The photosensitive sheet 8' on which the image is printed is separated from the original by the action of the suction tank 10, developed at the developing station 11 and ejected onto the printed sheet receiving tray 12 as aforementioned.

The gripper means 9 which holds the original between its teeth 9A and 9B is restored to its starting position as shown in FIG. I and temporarily stops there. The gripper means holding rings 18 remain stationary in their starting positions till the trailing end portion of the original superposed on the photosensitive sheet as a unit passes by the sensing means 32 which supplies a signal to the counter 30 when the trailing end' portion passes by it. The signal causes the gripper means holding ringsl8 to start rotating in synchronism with the printing cylinder 1. Immediately before the rings 18 start rotating, the next following photosensitive sheet is delivered to the position shown in FIG. 2 and the original 7 is superposed on the photosensitive sheet, so that printing of an image of the original on the photosensitive sheet is effected in the same manner as aforementioned.

Upon completion'of printing of images ofthe original on a predetermined number of copy sheets at which the machine is set, a signal is produced by the counter 30 and a current is passed to the solenoid 29 which is energized and causes its plunger 29A to move outwardly as shown in solid lines in FIG. 7. This brings the control lever 27 and arm 24 to their solid line positions in FIG. 7 and brings the gripper means 9 to an open position. Thus, the original 7 is released from between the teeth 9A and 93 as shown in FIG. 4 and brought into pressing engagement with the belt 13 by the action of the suction tank 14 and ejected onto the original-discharging tray 15. The gripper means 9 stands by in its position shown in FIG. 1 and FIG. 2 pending the insertion of another original.

From the foregoing description, it will be appreciated that the provision, in a copying machine of the penetration printing type, of gripper means for holding the leading end portion of the original which is adapted to rotate in synchronism with the printing cylinder permits acceptable duplicates to be produced without the original being deflected from its path of movement or inclined in its position during its movement even if a large number of duplicates are produced from a single copy because the original is firmly held at its leading end portion by the gripper means.

The provision of means for causing the gripper means holding the leading end portion of the original to remain stationary in its starting position without performing a repeat cycle till the passing of the trailing end portion of the original by a certain position on the printing cylinder permits duplicates of an original having a length greater than the outer circumference of the printing cylinder to be produced in a repeat operation without any trouble.

It is to be understood that the invention is not limited to the features and embodiments hereinabove specifically set forth, but may be carried out in other ways without departure from its spirit.

What I claim is:

1. A duplicating machine of the penetration printing type comprising a. a printing cylinder;

b. a belt passing around the outer periphery of said printing cylinder for rotating the same and conveying a photosensitive sheet and an original superposed one on the other as a unit;

c. means for automatically feeding photosensitive sheets; and

d. repeat means for defining an original circulating path;

wherein the improvement comprises:

e. gripper means comprising teeth for holding the leading end portion of an original therebetween and rotatable in synchronism with the printing cylinder along the outer periphery thereof, said gripper means comprising two sets of teeth and adapted to be brought to an open position and a closed position by a signal; means for sensing the passing of the trailing end portion of an original arranged in the path of movement of the original and a photosensitive sheet superposed one on the other as a unit, and

g. means for causing the gripper means holding the leading end portion of the original to remain stationary in its starting position until said sensing means senses the passing of the trailing end portion of the orignal by it.

2. A duplicating machine of the penetration printing type comprising a. a printing cylinder;

b. a belt passing around the outer periphery of said printing cylinder for rotating the same and conveying a photosensitive sheet and an original superposed one on the other as a unit;

c. means for automatically feeding photosensitive sheets; and

(1. repeat means for defining an original circulating path;

wherein the improvement comprises:

e. gripper means comprising teeth for holding the leading end portion of an original therebetween and rotatable in synchronism with the printing cylinder along the outer periphery thereof, said gripper means comprising two sets of teeth and adapted to be brought to an open position and a 5 closed position by a signal;

f. a plurality of rings for holding said gripper means, adapted to rotate in synchronism with the printing cylinder;

g. a shaft rotatably mounted on said gripper meansholding rings and having one of said sets of teeth of the gripper means firmly secured thereto, while pivotally supporting the other said set of teeth;

h. an arm firmly secured to one end of said shaft and normally biased to keep the gripper means in a closed position; and

i. gripper means-actuating means comprising a solenoid controlled by signals, and a control lever adapted to keep the gripper means in a closed position when said solenoid is de-energized but actuated when the solenoid is energized by a signal to move to a position in which it brings the gripper means to an open position.

3. A copying machine as defined in claim 2, wherein two sets of said gripper means-actuating means are provided, one set being arranged at a position in which the original is mounted on the printing cylinder and the other set being arranged in a position in which the original transfers from the printing cylinder to an originaldischarging belt, said one set of gripper meansactuating means performing the operation of holding the leading end portion of the original between the teeth of the gripper means and the other set performing the operation of releasing the leading end portion of the original from between the teeth of the gripper means.

4. A copying machine including a. means including a rotatable cylinder for reproducing an original sheet on a copy sheet when the original and copy sheets are held in superposed relation on the cylinder;

b. a driven belt passing partially around and urged against said cylinder for pressing an original sheet and a copy sheet against said cylinder in superposed relation while rotating said cylinder;

c. means for guiding an original sheet to astarting position for advance around said cylinder; and

(1. means for feeding a copy sheet to a position for ad vance around said cylinder in superposed relation to said original sheet;

wherein the improvement comprises e. means for gripping the leading edge of an original sheet to hold said original sheet during advance thereof around'said cylinder, said gripping means comprising teeth operable to grip and to release the original sheet;

f. means supporting said gripping means for rotary movement in adjacent relation to, and in synchronism with rotation of, the periphery of said cylinder, said supporting means returning said gripping means to said starting position once in each revolution thereof;

g. means for operating said teeth to grip and to release an original sheet in response to control signals, said operating means initially operating said teeth to grip an original sheet guided to said starting position by said guiding means, and thereafter operating said teeth to release the same original sheet only in response to accomplishment of a predetermined number of revolutions of said gripping means, so that said gripping means continuously grips the original sheet for advance of the same repeatedly to said starting position and thence around the cylinder for a predetermined number of times, said operating means including means for sensing and counting the number of revolutions of the original sheet;

h. said copy sheet feeding means comprising means for feeding a new copy sheet as aforesaid each time the leading edge of an original sheet is advanced to said starting position by said gripping means;

i. said supporting means including signal-responsive means for advancing said gripping means through one complete revolution from and to said starting position and arresting said gripping means at said starting position; and

j. said sensing and counting means including means for sensing passage of the trailing end of an original sheet past a predetermined point in the path of advance thereof around said cylinder, and for producing, in response to the sensed passage of the original trailing end as aforesaid, a signal for actuating said-signal-responsive means to initiate a new cycle of revolution of said gripping means.

5. A machine as defined in claim 4, wherein said operating means includes first means for operating said teeth to grip an original sheet at said starting position, and second means for operating said teeth to release an original sheet at a locality spaced from said starting position in the path of sheet advance, and further including means disposed adjacent the last-mentioned locality for removing an original sheet from the path of sheet advance upon release of the original sheet by the teeth at said locality.

6. A machine as defined in claim 5, wherein said gripping means includes two sets of teeth relatively movable between sheet-gripping position and sheetreleasing position, means biasing said teeth into sheetgripping position, and an arm connected to one set of said teeth and displaceable to move said teeth to sheetreleasing position against the force of said biasing means; and wherein each of said first and second operating means comprises a movably mounted lever and means for moving said lever into a position for engaging and displacing said arm to move said teeth as aforesaid, in response to a control signal, as said arm is advanced by rotation of the gripping means into a position adjacent the lever.

7. In apparatus for effecting guided advance of sheet material, in combination,

a. a rotatable cylinder;

b. means for conducting a sheet along a path extending around the periphery of said cylinder, said conducting means including i. means for gripping the leading edge of a sheet during advance thereof along said path, said gripping means being movable between closed and open positions for respectively gripping and releasing the sheet,

ii. means for yieldably biasing said gripping means to closed position, and

iii. rotary means for carrying said gripping means cyclically along said path around the axis of the cylinder in synchronism with rotation of said cylinder; and

c. control means, disposed adjacent a locality of said path, for selectively effecting opening and closing movement of said gripping means upon advance thereof to said locality by said rotary means;

d. said rotary means including signal-responsive means for effecting a single revolution of said gripping means about the axis of the cylinder in response to a control signal and for arresting advance of said gripping means upon completion of the single revolution; and

e. means for generating a control signal, for actuating said signal-responsive means to initiate a revolution of said gripping means, in response to passage of the trailing edge of a sheet past a predetermined point in saidpath. 

1. A duplicating machine of the penetration printing type comprising a. a printing cylinder; b. a belt passing around the outer periphery of said printing cylinder for rotating the same and conveying a photosensitive sheet and an original superposed one on the other as a unit; c. means for automatically feeding photosensitive sheets; and d. repeat means for defining an original circulating path; wherein the improvement comprises: e. gripper means comprising teeth for holding the leading end portion of an original therebetween and rotatable in synchronism with the printing cylinder along the outer periphery thereof, said gripper means comprising two sets of teeth and adapted to be brought to an open position and a closed position by a signal; f. means for sensing the passing of the trailing end portion of an original arranged in the path of movement of the original and a photosensitive sheet superposed one on the other as a unit, and g. means for causing the gripper means holding the leading end portion of the original to remain stationary in its starting position until said sensing means senses the passing of the trailing end portion of the orignal by it.
 2. A duplicating machine of the penetration printing type comprising a. a printing cylinder; b. a belt passing around the outer periphery of said printing cylinder for rotating the same and conveying a photosensitive sheet and an original superposed one on the other as a unit; c. means for automatically feeding photosensitive sheets; and d. repeat means for defining an original circulating path; wherein the improvement comprises: e. gripper means comprising teeth for holding the leading end portion of an original therebetween and rotatable in synchronism with the printing cylinder along the outer periphery thereof, said gripper means comprising two sets of teeth and adapted to be brought to an open position and a closed position by a signal; f. a plurality of rings for holding said gripper means, adapted to rotate in synchronism with the printing cylinder; g. a shaft rotatably mounted on said gripper means-holding rings and having one of said sets of teeth of the gripper means firmly secured thereto, while pivotally supporting the other said set of teeth; h. an arm firmly secured to one end of said shaft and normally biased to keep the gripper means in a closed position; and i. gripper means-actuating means comprising a solenoid controlled by signals, and a control lever adapted to keep the gripper means in a closed position when said solenoid is de-energized but actuated when the solenoid is energized by a signal to move to a position in which it brings the gripper means to an open position.
 3. A copying machine as defined in claim 2, wherein two sets of said gripper means-actuating means are provided, one set being arranged at a position in which the original is mounted on the printing cylinder and the other set being arranged in a position in which the original transfers from the printing cylinder to an original-discharging belt, said one set of gripper means-actuating means performing the operation of holding the leading end portion of the original between the teeth of the gripper means and the other set performing the operation of releasing the leading end portion of the original from between the teeth of the gripper means.
 4. A copying machine including a. means including a rotatable cylinder for reproducing an original sheet on a copy sheet when the original and copy sheets are held in superposed relation on the cylinder; b. a driven belt passing partially around and urged against said cylinder for pressing an original sheet and a copy sheet against said cylinder in superposed relation while rotating said cylinder; c. means for guiding an original sheet To a starting position for advance around said cylinder; and d. means for feeding a copy sheet to a position for advance around said cylinder in superposed relation to said original sheet; wherein the improvement comprises e. means for gripping the leading edge of an original sheet to hold said original sheet during advance thereof around said cylinder, said gripping means comprising teeth operable to grip and to release the original sheet; f. means supporting said gripping means for rotary movement in adjacent relation to, and in synchronism with rotation of, the periphery of said cylinder, said supporting means returning said gripping means to said starting position once in each revolution thereof; g. means for operating said teeth to grip and to release an original sheet in response to control signals, said operating means initially operating said teeth to grip an original sheet guided to said starting position by said guiding means, and thereafter operating said teeth to release the same original sheet only in response to accomplishment of a predetermined number of revolutions of said gripping means, so that said gripping means continuously grips the original sheet for advance of the same repeatedly to said starting position and thence around the cylinder for a predetermined number of times, said operating means including means for sensing and counting the number of revolutions of the original sheet; h. said copy sheet feeding means comprising means for feeding a new copy sheet as aforesaid each time the leading edge of an original sheet is advanced to said starting position by said gripping means; i. said supporting means including signal-responsive means for advancing said gripping means through one complete revolution from and to said starting position and arresting said gripping means at said starting position; and j. said sensing and counting means including means for sensing passage of the trailing end of an original sheet past a predetermined point in the path of advance thereof around said cylinder, and for producing, in response to the sensed passage of the original trailing end as aforesaid, a signal for actuating said signal-responsive means to initiate a new cycle of revolution of said gripping means.
 5. A machine as defined in claim 4, wherein said operating means includes first means for operating said teeth to grip an original sheet at said starting position, and second means for operating said teeth to release an original sheet at a locality spaced from said starting position in the path of sheet advance, and further including means disposed adjacent the last-mentioned locality for removing an original sheet from the path of sheet advance upon release of the original sheet by the teeth at said locality.
 6. A machine as defined in claim 5, wherein said gripping means includes two sets of teeth relatively movable between sheet-gripping position and sheet-releasing position, means biasing said teeth into sheet-gripping position, and an arm connected to one set of said teeth and displaceable to move said teeth to sheet-releasing position against the force of said biasing means; and wherein each of said first and second operating means comprises a movably mounted lever and means for moving said lever into a position for engaging and displacing said arm to move said teeth as aforesaid, in response to a control signal, as said arm is advanced by rotation of the gripping means into a position adjacent the lever.
 7. In apparatus for effecting guided advance of sheet material, in combination, a. a rotatable cylinder; b. means for conducting a sheet along a path extending around the periphery of said cylinder, said conducting means including i. means for gripping the leading edge of a sheet during advance thereof along said path, said gripping means being movable between closed and open positions for respectively gripping and releasing the sheet, ii. means for yieldably biasing said gripping means tO closed position, and iii. rotary means for carrying said gripping means cyclically along said path around the axis of the cylinder in synchronism with rotation of said cylinder; and c. control means, disposed adjacent a locality of said path, for selectively effecting opening and closing movement of said gripping means upon advance thereof to said locality by said rotary means; d. said rotary means including signal-responsive means for effecting a single revolution of said gripping means about the axis of the cylinder in response to a control signal and for arresting advance of said gripping means upon completion of the single revolution; and e. means for generating a control signal, for actuating said signal-responsive means to initiate a revolution of said gripping means, in response to passage of the trailing edge of a sheet past a predetermined point in said path. 